Percutaneous guidewire-directed catheters of many different types are used in a wide variety of medical procedures. These types include angioscopic catheters, angioplasty catheters, and genito-urinary catheters; some are intended for diagnostic purposes, some for dilatation purposes, and some for purposes of delivering a drug, contrast agent or other useful agent to an internal bodily vessel.
These various types of catheters contain numerous features affecting their ease and effectiveness of use. These features are most conveniently understood by examination of a single class of catheters--i.e., dilatation balloon catheters for angioplasty procedures. The following discussion will therefore focus on this one class, with the understanding however that the scope of this disclosure extends well beyond this class to encompass all guidewire-directed catheters.
In recent years, angioplasty has gained widespread acceptance and use as a technique for treating atherosclerotic coronary and peripheral vascular diseases. According to this technique, a dilatation balloon catheter-guidewire system is percutaneously introduced into the patient's vasculature under fluoroscopic control until the balloon component of the system spans the confines of a vascular stenosis. Once in position, the balloon is inflated by hydraulic pressure to dilate the stenosis and thereby relieve the obstruction to blood flow.
A feature of certain catheter-guidewire systems which is of considerable advantage in angioplasty procedures is "exchangeability." This is the ability of the guidewire and the catheter body to be separated while inside the vasculature for purposes of removing one or the other and replacing the removed component with a substitute component which differs in some respect. The need for such an exchange arises when a component originally placed inside the vasculature is discovered subsequent to its placement to be inadequate or inappropriate for a particular stenosis. Systems having the capability of this exchange are termed "exchangeable" systems, and those in which the catheter body can be exchanged without removing the guidewire are termed "over-the-wire" systems. In exchangeable systems, either the catheter body, the guidewire or both can be replaced without the need to reestablish intraluminal access. This saves time and, in so doing, lowers the risk of patient injury due to prolonged interference with the patient's blood flow from the presence of the catheter in the vasculature. Because of this advantage as well as their inherently greater steerability, exchangeable systems command approximately 80% of the angioplasty catheter market.
While non-exchangeable systems can be constructed with single lumens, all exchangeable, and particularly over-the-wire, systems in current use contain at least two lumens, one for the guidewire and the other for the inflation fluid used to inflate the balloon. The guidewire lumen provides the guidewire with full mobility relative to the catheter body and vice versa while preventing loss of inflation fluid from both the balloon and the inflation lumen which supplies the fluid under pressure to the balloon. In some constructions, the inflation lumen is an annular lumen surrounding the guidewire lumen, whereas in others the two are side by side.
The presence of multiple lumens gives over-the-wire systems a larger cross section, however, raising the degree to which the system will impair the flow of blood and other fluids through the vasculature. This raises the risks of ischemia, of compromising the resolution of intraoperative angiography, and of interference with the intraoperative administration of therapeutic agents. For this reason, both lumens as well as the overall profile of the catheter body are designed to have as small a cross section as possible.
The development of new materials for the catheter body has led to considerable reductions in the catheter body cross section. These materials permit thinner walls and smaller caliber channels without loss of strength, function or structural integrity. There is a limit to how much the inner diameter of the guidewire channel can be reduced, however. One reason among several is that the distal segment of the guidewire is covered with a coil to provide this segment with the combination of structural strength and flexibility it needs for steering through the vasculature. While the diameter of the coil may be the same as or small than that of the proximal, full-diameter portion of the guidewire which is not covered by the coil, the coil most often limits the degree to which the diameter of the guidewire and hence the diameter of the guidewire lumen can be reduced.
Friction between the guidewire and the inner wall of the guidewire lumen is also a problem. With long guidewires and narrow lumens, it is particularly difficult in many cases to advance the catheter body over the guidewire.
Small caliber tubing may be constructed of lubricious materials such as polytetrafluoroethylene or polyethylene, which suggests the possibility of using such tubing as the guidewire lumen, while the annular space between the tubing and the catheter body serves as the inflation lumen. This is not a suitable arrangement, however, since it requires that the lubricious tubing be bonded to the balloon at the distal balloon orifice. Lubricious materials do not bond well to other materials, and as a result the bond will not be a strong one. A strong bond is indeed needed at this location, since the pressure in the balloon would otherwise tend to separate the balloon from the tubing. Failure of the bond in this manner would result in escape of the inflation fluid into the vasculature.
For these and other reasons, there exists a need for a catheter body for over-the-wire catheters which contains tubing for the guidewire lumen which is both lubricious and capable of bonding securely to the balloon.